The present invention is directed to a dental handpiece which has a drive motor part and a handpiece part which is mounted for rotation on a longitudinal axis of the motor part. The handpiece part contains a first section, which is releasably secured for rotation on the drive motor part and supports a drive train for transferring rotary motion of the drive motor to a socket in a head part, which socket mounts a tool for rotary motion on the axis of the tool. Cooling lines extend through the motor part and a rotary coupling into the first section and then to the head part for discharge adjacent to the so claimed tool. The rotatable coupling is in the rotational joint between a portion of the first section and the motor part and includes an annular groove in one of the two rotatable members and a passage in the other member in communication with the groove.
Dental handpieces, which have a drive motor part, a handpiece part, which is composed of a first section mounted for rotation on the longitudinal axis of the motor part and has a head portion at the other end with a drive train which is formed of drive shaft sections for conveying the rotary motion of the drive motor to a socket which mounts a tool for rotation on an axis, are known. A rotational connection between the first section and the motor part is usually formed by means of a snap ring groove which on one hand insures rotatably but prevents axial shifting of the first section on the drive motor part. The cooling agent transmission lines from the drive motor to the handpiece part employs a rotatable coupling at the rotational connection or rotary joint therebetween. The rotatable coupling essentially consists of an annular groove for each cooling agent line which groove is sealed on both sides by means of O rings and is in communication with a passageway of the other part. For example, the annular groove may be provided in a guide shank which surrounds the drive shaft of the drive motor and an axial or radial channels are in communication with the annular groove and are formed in the other part which is telescopically received onto the guide shank. A reverse arrangement of the rotatable coupling parts is also possible so that the annular groove are on the handpiece part which is telescoped onto the guide shank which is provided with radial channels.
In these dental handpieces, the rotatable coupling is also released when the two handpiece parts, for example the first section is removed or disconnected from the drive motor part. The coupling and uncoupling of the handpiece parts, which is carried out frequently in order to change the various head pieces used with a drive motor, cause a great wear of the rotatable coupling parts, particularly at the O ring seals. Moreover, while in an uncoupled state, there is a danger that dirt can penetrate into the openings of the radial passages and into the annular grooves of the rotatable coupling to the detriment of the flow of the cooling agent which may be interrupted by these particles.
Another problem is present by the requirements for sterilization particularly sterilization of the head part and the grip section which sterilization is accomplished in an autoclave. Thus, the sealing rings are subjected to high temperatures which are detrimental to their sealing capabilities and in addition, glued joints which are often present at the bearings may be damaged and the bearing lubricants may be washed away. Due to the washing out of the lubricants for the bearings during the sterilization operation, the bearings must be lubricated after every sterilization process.